High density direct connect LOC assembly

ABSTRACT

An apparatus and method for attaching a semiconductor die to a lead frame wherein the electric contact points of the semiconductor die are relocated to the periphery of the semiconductor die through a plurality of conductive traces. A plurality of leads extends from the lead frame over the conductive traces proximate the semiconductor die periphery and directly attaches to and makes electrical contact with the conductive traces in a LOC arrangement. Alternately, a connector may contact a portion of the conductive trace to make contact therewith.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/109,133,filed Apr. 5, 2005, pending, which is a continuation of application Ser.No. 10/366,769, filed Feb. 14, 2003, now U.S. Pat. No. 6,882,033, issuedApr. 19, 2005, which is a continuation of application Ser. No.09/649,803, filed Aug. 28, 2000, now U.S. Pat. No. 6,531,761, issuedMar. 11, 2003, which is a divisional of application Ser. No. 09/026,839,filed Feb. 20, 1998, now U.S. Pat. No. 6,335,225, issued Jan. 1, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for attaching asemiconductor die to a lead frame or other type of connector. Moreparticularly, the present invention relates to relocating electriccontact points of a semiconductor die to the periphery of thesemiconductor die through a plurality of conductive traces. The leads ofthe lead frame extend over the conductive traces proximate thesemiconductor periphery and directly attach to and make electricalcontact with the conductive traces in a variety of arrangements orconfigurations. Alternately, a connector may be used to contact aportion of the end of a conductive trace located at the periphery of asemiconductor die.

2. State of the Art

Higher performance, lower cost, increased miniaturization of components,and greater packaging density of integrated circuits are goals of thecomputer industry. Greater integrated circuit density is primarilylimited by the space or “real estate” available for mounting asemiconductor die on a substrate such as a printed circuit board.Conventional lead frame design inherently limits package density for agiven semiconductor die size because the die-attach paddle of the leadframe must be larger than the die to which it is bonded. The larger thesemiconductor die, the less space that remains around the periphery ofthe die-bonding pad for wire bonding. Furthermore, the wire bonding padson the standard lead frame provide anchorage for the leads when theleads and the semiconductor die are encapsulated in plastic. Therefore,as the die size is increased in relation to a given package size, thereis a corresponding reduction in the space along the sides of the packagefor the encapsulating plastic which joins the top and bottom of theplastic body at the mold part line and anchors the leads. Thus, as theleads and encapsulant are subjected to the normal stresses of subsequentforming and assembly operations, the encapsulating plastic may crack,compromising package integrity and substantially increasing theprobability of premature device failure.

Also, since lead frames are designed for use with a semiconductor diehaving a specific pattern of bond pads located on the active surfacethereof, it is desirable to have the flexibility of changing the bondpad locations of a die so that an existing lead frame design may be usedwith differing types of die material.

For example, one method of chip attachment which reduces the die size isa so-called “leads-over-chip” (“LOC”) arrangement. Conventional LOCdevices have a plurality of leads disposed on and attached to an activesurface of a semiconductor die, thus the name leads-over-chip. A primaryadvantage of LOC is that the ratio between the size of the semiconductordie and the size of a package which encapsulates the semiconductor dieis high. This advantage is achieved because the die-attach paddle is notrequired since the semiconductor die is instead attached to the leads.

U.S. Pat. No. 4,862,245 issued Aug. 29, 1989 to Pashby et al. (“the '245patent”) illustrates a LOC arrangement on a semiconductor die (see FIG.10). The leads 16 are extended over a semiconductor die 10 toward acentral or axial line of bond pads 14 wherein bond wires 12 make theelectrical connection between the inner ends of leads 16 and the bondpads 14. In wire bonding, the bond wires 12 are attached, one at a time,to each bond pad 14 on the semiconductor die 10 and extend to acorresponding lead or trace end 16 on a lead frame or printed circuitboard (not shown). The bond wires 12 are generally attached through oneof three industry-standard wire bonding techniques: ultrasonic bonding,using a combination of pressure and ultrasonic vibration bursts to forma metallurgical cold weld; thermocompression bonding, using acombination of pressure and elevated temperature to form a weld; andthermosonic bonding, using a combination of pressure, elevatedtemperature, and ultrasonic vibration bursts. Film-type alpha barriers18 are provided between the semiconductor die 10 and the leads 16, andare adhered to both, thus eliminating the need for a separate die paddleor other die support aside from the leads 16 themselves. Theconfiguration of the '245 patent assists in limiting the ingress ofcorrosive environmental contaminants to the active surface of the die,achieves a larger portion of the circuit path length encapsulated in thepackaging material applied after wire bonding, and reduces electricalresistance caused by the bond wires 12 by placing the lead ends incloser proximity to the bond pads 14 (i.e., the longer the bond wire,the higher the resistance). Although this configuration offers certainadvantages, it requires that bond wires 12 be individually attachedbetween the bond pads 14 and the leads 16. Bond wires have an inherentproblem called bond wire sweep. When encapsulating a bare die assembly,the die assembly is generally placed in a mold with a molten encasingmaterial being injected into the mold whereby the encasing materialsurrounds the die assembly and the material conforms to the mold.However, this process causes stresses on the bond wires. Since themolten encasing material is viscous, it tends to place directionalforces on the bond wires as the encasing material is injected into themold. These directional forces cause the bond wires to stretch, whichcan, in turn, cause the bond wires to short with adjacent bond wires orbond pads or be pulled from a bond pad or lead to which the wires arebonded.

U.S. Pat. No. 5,252,853 issued Oct. 12, 1993 to Michii illustrates a LOCarrangement on the semiconductor die which does not use bond wires (seeFIG. 11). The leads 22 are extended over a semiconductor die 20 towardcentrally located bond pads 24 (shown in shadow). The leads 22 extend toa position over their respective bond pads 24 wherein the leads 22 arebonded directly to their bond pads 24 with TAB attachment. Although thisdirect bonding of the lead to the bond pad eliminates the need for wirebonding, it still requires lengthy leads to make electrical contactbetween the bond pads and the lead frame. Film-type alpha barriers 26are also provided between the semiconductor die 20 and the leads 22.

Therefore, it would be advantageous to develop a technique and a devicefor increasing integrated circuit density by reducing lead width andreducing bond pad size, using non-complex lead frame configurations andeliminating bond wires, while using commercially available, widelypracticed semiconductor device fabrication techniques.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to an apparatus and method for attaching asemiconductor die to a lead frame or other type of connector, such as aclip type. Electric contact points of the semiconductor die of thepresent invention are relocated to the periphery of a semiconductor dieand are in electrical contact with a lead frame or connector. Thesemiconductor die may be in electrical contact with a lead frame throughat least one lead which extends over and directly attaches to itsrespective electric contact point on the semiconductor die periphery, orthrough one lead which extends over and is attached to a die contactpoint with electrical contact being made to the electrical contact pointof the die by means of a wire bond, or through one lead which extendsadjacent the edge of a die with electrical contact being made to theelectrical contact point of the die by means of a wire bond.

The apparatus is constructed by first forming a semiconductor die on asemiconductor wafer. A plurality of electric contact points, such asbond pads, is disposed on an active surface of the semiconductor die. Aplurality of conductive traces is formed on the semiconductor die activesurface to make a conductive route between each electric contact pointand a position proximate to the semiconductor die periphery. A pluralityof edge electric contact points may be formed on the periphery of thesemiconductor die active surface during the formation of the conductivetraces.

The conductive traces can be formed by a number of industry standardtechniques, such as: depositing a conductive material on the activesurface of the semiconductor die, patterning, and etching the conductivematerial; depositing a conductive paste on the semiconductor die activesurface by silk screening the conductive traces directly thereon;directly extruding a conductive paste to form the conductive traces, orapplying an insulative material on the semiconductor die active surface,etching a trough in the insulative material, filling the trough with aconductive material, and removing the excess material. These methods areless expensive than relocating the electric contact points during thesemiconductor die fabrication process.

Although the formation of the conductive traces is preferably carriedout on the semiconductor wafer, it is understood that the traces can beformed on each semiconductor die after the semiconductor dice have beencut from the semiconductor wafer.

After the electrical traces have been formed on the semiconductor dieand the semiconductor die has been cut from the semiconductor wafer, alead frame is attached to the semiconductor die. In one instance, aplurality of leads from the lead frame is attached directly to and formsan electrical contact with the edge electric contact points of thesemiconductor die. The direct attachment of the leads eliminates theneed for bond wires, which reduces the cost of the apparatus. In anotherinstance, a plurality of leads from the lead frame is directly attachedto the die with electrical contact being made to the contact points ofthe semiconductor die by means of wire bonds. In yet another instance, aplurality of leads from the lead frame is terminated adjacent an edge ofthe semiconductor die with electrical contact being made with contactpoints of the semiconductor die by means of connectors.

In one instance, since the present invention provides neither adie-attach paddle nor a plurality of lengthy leads to provide supportfor both the semiconductor die and attached lead frame, thesemiconductor device fabrication technique for the semiconductor die ofthe present invention may have to be slightly modified over presentsemiconductor device fabrication techniques to ensure that no stresseson the lead frame attached semiconductor die occur prior to theencapsulation step. Such a fabrication technique modification mayinclude providing clips on the lead frame to hold the semiconductor die.Although modifying the fabrication process is a disadvantage, thedisadvantage is far outweighed by the benefits realized by the presentinvention. Since the leads are not required to provide support, they canbe designed to be narrower in width. The narrower lead width allows theedge electric contact points to be smaller than relocated electricalcontact points. The smaller edge electric contact points allow thesemiconductor die size to be reduced or allow a greater number of edgeelectric contact points to be placed on the semiconductor die periphery.The narrower lead width also results in a smaller lead pitch whichserves to reduce the cost of the apparatus. Furthermore, attachment ofthe leads at the semiconductor die periphery eliminates the need for afilm-type alpha barrier between the semiconductor die and the lead,which further reduces the semiconductor die cost.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention can be more readily ascertained fromthe following description of the invention when read in conjunction withthe accompanying drawings, in which:

FIGS. 1 a-1 g are full and partial views of a first preferred method offorming conductive traces on the semiconductor die of the presentinvention in wafer form or individual die form;

FIGS. 2 a-2 c are partial views of a second preferred method of formingconductive traces on the semiconductor die of the present invention;

FIGS. 3 a-3 c are partial views of a third preferred method of formingconductive traces on the semiconductor die of the present invention;

FIGS. 4 a-4 d are partial views of a fourth preferred method of formingconductive traces on the semiconductor die of the present invention;

FIG. 5 is a top view of a lead arrangement of the present invention;

FIG. 6 is a top view of a first alternative lead arrangement of thepresent invention;

FIG. 7 is a view of an alternative connector arrangement of the presentinvention;

FIG. 8 is a view of an alternative connector arrangement of the presentinvention;

FIG. 9 is a view of an alternative connector arrangement of the presentinvention;

FIG. 10 is a top view of a prior art semiconductor die assembly usingleads extending onto the semiconductor die and using bond wires toconnect the leads to the bond pads prior to the encapsulation of thesemiconductor die in a protective coating; and

FIG. 11 is a top view of a prior art semiconductor die assembly usingleads extending onto the semiconductor die to directly connect to thebond pads prior to the encapsulation of the semiconductor die in aprotective coating.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 a-1 g illustrate a first method of forming conductive traces ona semiconductor die 100 of the present invention. FIG. 1 a illustrates aplurality of semiconductor die 100 located on a wafer 1000, eachsemiconductor die 100 having a periphery 101 defined, in general, by thestreet areas 103 located therebetween of the wafer 1000. Eachsemiconductor die 100 has conductive traces 116 on an active surfacethereof connecting the bond pads 104 of the die to the periphery 101 ofthe semiconductor die 100. FIG. 1 b illustrates a silicon substrate 102having circuitry (not shown) disposed on an active surface. Thecircuitry of the silicon substrate 102 receives input and/or distributesoutput via bond pads 104 or electric contact points disposed on thesemiconductor die active surface. A passivation layer 106 is generallyapplied over the semiconductor die active surface with the bond pads 104exposed. As shown in FIG. 1 c, a layer of conductive material 108 isapplied over the passivation layer 106, making electrical contact withthe bond pads 104. A layer of etch resist material 110 is applied overthe layer of conductive material 108, as shown in FIG. 1 d. The etchresist material layer 110 is then masked and etched to form a tracepattern 112 which extends from the bond pads (not shown) to an edge 114of the silicon substrate 102 and exposing a portion of the conductivematerial layer 108, as shown in FIG. 1 e. The conductive material layer108 is then etched, as shown in FIG. 1 f, wherein the trace pattern 112acts as a mask to form a conductive trace 116 from the conductivematerial layer 108. As shown in FIG. 1 g, the trace pattern 112 isstripped to expose the conductive trace 116. The conductive trace 116may have a landing portion 118 proximate to the silicon substrate edge114. The landing portion 118 may be slightly wider than the conductivetrace 116 and serves as the contact sight to attach a lead (not shown)from a lead frame (not shown).

FIGS. 2 a-2 c illustrate a second method of forming conductive traces ona semiconductor die 200 of the present invention. FIG. 2 a illustrates asilicon substrate 202 having circuitry (not shown) disposed on an activesurface. The circuitry of the silicon substrate 202 receives inputand/or distributes output via bond pads or electric contact points 204disposed on the semiconductor die active surface. A passivation layer206 is generally applied over the semiconductor die active surface withthe contact points 204 exposed. As shown in FIG. 2 b, a silk screen 208is placed over the passivation layer 206. The silk screen 208 has apermeable portion 210 in the shape of a desired conductive trace. Thesilk screen permeable portion 210 allows a substantially liquidconductive material to pass therethrough and attach to the passivationlayer 206 to form a conductive trace 212, as shown in FIG. 2 c, whichmakes electrical contact with the contact points 204 and extends to anedge 214 of the silicon substrate 202.

FIGS. 3 a-3 c illustrate a third method of forming conductive traces ona semiconductor die 300 of the present invention. FIG. 3 a illustrates asilicon substrate 302 having circuitry (not shown) disposed on an activesurface. The circuitry of the silicon substrate 302 receives inputand/or distributes output via bond pads or electric contact points 304disposed on the semiconductor die active surface. A passivation layer306 is generally applied over the semiconductor die active surface withthe contact points 304 exposed. As shown in FIG. 3 b, an extrusionnozzle 308 extrudes a viscous conductive material 310 directly onto thepassivation layer 306. The viscous conductive material 310 forms aconductive trace 312 between the contact points 304 and an edge 314 ofthe silicon substrate 302, as shown in FIG. 3 c.

FIGS. 4 a-4 d illustrate a fourth method of forming conductive traces onthe semiconductor die 400 of the present invention. FIG. 4 a illustratesa silicon substrate 402 having circuitry (not shown) disposed on anactive surface. The circuitry of the silicon substrate 402 receivesinput and/or issues output via bond pads or electric contact points 404disposed on the semiconductor die active surface. A passivation layer406 is generally applied over the semiconductor die active surface withthe contact points 404 exposed. As shown in FIG. 4 b, a layer of etchresist material 408 is applied over the passivation layer 406. The etchresist material layer 408 is then masked and etched to form a recessedconductive trace pattern 410 which exposes the contact points 404 andextends to an edge 412 of the silicon substrate 402, as shown in FIG. 4c. A conductive material is disposed within the recessed conductivetrace pattern 410 which forms a conductive trace 414, as shown in FIG. 4d.

FIG. 5 illustrates a semiconductor assembly 500 of the presentinvention. The semiconductor assembly 500 comprises a lead frame 502having a plurality of leads 504 extending therefrom. The leads 504extend to a periphery 506 of semiconductor die 508 wherein the leads 504extend over, directly attach to, and make electrical contact with aplurality of respective conductive traces 510 which is attached to thesemiconductor die 508. The conductive traces 510 each terminateproximate to the semiconductor die periphery 506 and extend to makeelectrical contact with a plurality of bond pads or electrical contactpoints 512 (shown in shadow) disposed on the semiconductor die 508.

FIG. 6 illustrates an alternative semiconductor assembly 600 of thepresent invention. The alternative semiconductor assembly 600 is similarto the semiconductor assembly 500 of FIG. 5; therefore, componentscommon to FIGS. 5 and 6 retain the same numeric designation. Thedifference between the alternative semiconductor assembly 600 and thesemiconductor assembly 500 is that the bond pads 602 are variablydisposed on the semiconductor die 508, rather than in linear rows, asshown in FIG. 5 for bond pads 512. Thus, the conductive traces 604 foralternative semiconductor assembly 600 are of variable shape andconfiguration in order to route the conductive traces 604 to theirappropriate position on the semiconductor die periphery 506.

Referring to drawing FIG. 7, a semiconductor die 100 is illustratedhaving a conductive trace 414 extending to the periphery 101 of thesemiconductor die 100. Making electrical contact with a portion of thesecond end of the conductive trace 414 is a portion of a connector 700.The connector 700 resiliently abuts the periphery 101 of thesemiconductor die 100, making contact with a portion of the second endof conductive trace 414. The connector 700 may be any suitable type,such as a clip-type connector, to resiliently engage the conductivetrace 414 of the semiconductor die 100. Any desired number of connectors700 may be used for such a purpose. Further, if desired, the connector700 may be resiliently biased through the use of springs, elastomers,etc. in contact with conductive trace 414.

Referring to drawing FIG. 8, a connector 702 is illustrated makingcontact with a portion of the second end of the conductive trace 414 anda portion of the upper surface of the conductive trace 414 adjacent theperiphery 101 of the semiconductor die 100. The connector 702 may be ofany suitable type and may be used in any desired number to connect theconductive traces 414 of the semiconductor die 100 to a substrate.Further, the connector 702 may be resiliently biased into engagementwith the conductive trace 414.

Referring to drawing FIG. 9, a connector 702 is illustrated makingcontact with a portion of the second end of the conductive trace 414 anda portion of the upper surface of the conductive trace 414 adjacent theperiphery 101 of the semiconductor die 100. The connector 702 may be ofany suitable type and may be used in any desired number to connect theconductive traces 414 of the semiconductor die 100 to a substrate 402.Also illustrated is a portion 710 resiliently contacting the opposedsurface 100N of the semiconductor die 100 to resiliently bias theconnector 702 into contact with conductive trace 414. The portion 710may be part of a suitable connector or a portion of connector 702, etc.Alternately, the portion 710 may bear against the exterior of connector702 (shown in phantom lines) to bias the connector 702 against theconductive trace 414 at the periphery 101 of the semiconductor die 100.

Having thus described in detail preferred embodiments of the presentinvention, it is to be understood that the invention defined by theappended claims is not to be limited by particular details set forth inthe above description as many apparent variations thereof are possiblewithout departing from the spirit or scope thereof.

1. An assembly comprising: a semiconductor die having a periphery and anactive surface having a plurality of electric contact points disposed onthe active surface; and a plurality of conductive traces on the activesurface, each conductive trace of the plurality of conductive tracescomprising a first end electrically contacting at least one electriccontact point of the plurality of electric contact points and a secondend terminating proximate the semiconductor die periphery, eachconductive trace comprising a trace of extruded conductive material onthe active surface between the at least one semiconductor die electriccontact point making contact therewith and the periphery of thesemiconductor die.
 2. The assembly of claim 1, further comprising aplurality of leads of a lead frame resiliently connected to and inelectrical communication with portions of the second ends of theplurality of conductive traces.
 3. The assembly of claim 1, wherein thesemiconductor die comprises one semiconductor die of a plurality ofsemiconductor dice on a wafer.
 4. A plurality of semiconductor dice on awafer, comprising: a plurality of semiconductor dice located on thewafer, each semiconductor die having a periphery and an active surfacewith at least one electric contact point disposed on the active surface;and at least one conductive trace on the active surface, the at leastone conductive trace comprising a first end electrically contacting theat least one semiconductor die electric contact point and a second endterminating proximate the semiconductor die periphery, the at least oneconductive trace comprising a trace of extruded conductive material onthe active surface between the at least one electric contact pointmaking contact therewith and the periphery of the semiconductor die toexpose a portion of the at least one conductive trace at a portion ofthe periphery of the semiconductor die.